1. Field of the Invention
The present invention relates to a fuel spacer of separate cell type used for supporting a fuel assembly in a nuclear reactor, and a manufacturing method therefor.
2. Description of the Prior Art
U.S. Pat. No. 4,508,679 discloses a fuel spacer of separate cell type for supporting a fuel assembly in a nuclear reactor. This fuel spacer is composed of a number of cylindrical members or separate cells for receiving fuel rods therein. These cylindrical members are arranged in a square array with adjacent members welded to each other in those contact portion, and the periphery of the group of the arrayed members is surrounded by side bands which are also welded to cylindrical members in the contact portion thereof. To support a fuel rod, each of the cylindrical members is mounted with a spring and formed with projections on its inner surface.
As seen in FIGS. 3A, 3B and 3C which show a fuel spacer disclosed in the above U.S. Patent, the side wall of the cylindrical member 3 is formed with a slit 7 of laid-U shape for receiving a spring and with linear slits 9 for forming projections 5.
The spring for this fuel spacer is a leaf spring of a continuous loop type formed into a circular ring having a sectional rhombic shape. When the spring is fitted to one cylindrical member 3, one half member of the loop type spring is inserted through the slit 7 of laid-U shape into inside of one cylindrical member 3, and then the cylindrical member is rotated relative to the spring so that the overhang portion 8 formed with the slit 7 of laid-U shape of the side wall may enter into one opening of the spring 4 of loop type, causing the portion 8 to be covered by the leaf spring. Next, another cylindrical member is positioned adjacent to said one cylindrical member with their slits 7 of laid-U shape opposing to each other, and rotated relative to the spring in the different direction so that its overhang portion 8 may also enter into other opening of the same loop type spring. Thus, one half of the spring inserts into inside of one cylindrical member, while another half of the same inserts into inside of the other adjacent cylindrical member. In this situation of the cylindrical members and the spring, the adjacent cylindrical members are connected with each other by welding at their upper and lower ends, keeping the spring to the cylindrical members.
A number of paired cylindrical members thus combined with each other are so arranged to form a square array of cylindrical members as mentioned above, and each of the cylindrical members in the array is connected with adjacent cylindrical members by welding at their contact portions, only excluding connections between the paired members which have been already welded to each other for securing the spring. At the same time, side bands are disposed around the group of the arrayed cylindrical members, and connected to adjacent cylindrical members by welding at their contact portions.
In the assembly process by the use of welding for such a fuel spacer of separate cell type as mentioned above, in consideration of the spacer function of supporting fuel rods, it is much required to locate the cylindrical members at exact positions and in exact directions without requiring any difficult work. With respect to this subject, there is found no prior art sufficiently attending thereto, yet.